9,793 research outputs found
Understanding reverse osmosis polyamide active layer macrostructure and performance through indirect microscopic observation of film growth
Given the random nature of reverse osmosis polyamide macrostructure, it is difficult to understand the relationship between its structure and its separation characteristics. Many have addressed this subject and a few have reached significant conclusions to date. Acknowledging that membrane chemistry is the most important lever in controlling performance and not structure, to truly understand which features of the polyamide film can be manipulated to affect performance, there may be value in understanding its formation mechanism. Building upon a basic grasp of this mechanism, it may be possible to fine tune membrane performance through structure manipulation.
While direct observation of polyamide film growth is not yet possible on a microscopic scale, new methods have been developed for indirect observation of the process. These methods, pseudo-stop-motion imaging and reactive post-polymerization potting, have provided valuable insight on the formation mechanism. The pseudo-stop-motion imaging technique was developed to view the polyamide structure on a microscopic scale at discrete points in time during the interfacial polymerization, from the first appearance of polyamide material on the support surface to the end of the polymerization. Essentially watching the process occur diminished the need for complex modeling to produce a basic growth hypothesis. Furthermore, the method can be used for any type of polyamide, and is limited only by the resolution of electron microscopy.
Reactive post-polymerization potting is a technique developed to understand the structure of polyamide in its as-formed state. Historical microscopy has been performed on dried membranes, but not on films immediately following polymerization. The resulting structures are strikingly different from those observed in the literature via SEM and TEM, and when taken in context with the growth mechanism proposed from pseudo-stop-motion imaging, it further supports a mechanism of polyp inflation rather than continuous film formation. Well-controlled pilot-scale polyamide casting has been performed to corroborate the proposed mechanistic theory, and the theory will be framed within the broader context of polyamide membrane development
Adjacency Matrices of Configuration Graphs
In 1960, Hoffman and Singleton \cite{HS60} solved a celebrated equation for
square matrices of order , which can be written as where , , and are the identity matrix, the
all one matrix, and a --matrix with all row and column sums equal to
, respectively. If is an incidence matrix of some configuration
of type , then the left-hand side is an adjacency matrix of the non--collinearity
graph of . In certain situations, is also an
incidence matrix of some configuration, namely the neighbourhood
geometry of introduced by Lef\`evre-Percsy, Percsy, and Leemans
\cite{LPPL}.
The matrix operator can be reiterated and we pose the problem of
solving the generalised Hoffman--Singleton equation . In
particular, we classify all --matrices with all row and column sums
equal to , for , which are solutions of this equation. As
a by--product, we obtain characterisations for incidence matrices of the
configuration in Kantor's list \cite{Kantor} and the
configuration #1971 in Betten and Betten's list \cite{BB99}
Dark matter annihilation and decay in dwarf spheroidal galaxies: The classical and ultrafaint dSphs
Dwarf spheroidal (dSph) galaxies are prime targets for present and future
gamma-ray telescopes hunting for indirect signals of particle dark matter. The
interpretation of the data requires careful assessment of their dark matter
content in order to derive robust constraints on candidate relic particles.
Here, we use an optimised spherical Jeans analysis to reconstruct the
`astrophysical factor' for both annihilating and decaying dark matter in 21
known dSphs. Improvements with respect to previous works are: (i) the use of
more flexible luminosity and anisotropy profiles to minimise biases, (ii) the
use of weak priors tailored on extensive sets of contamination-free mock data
to improve the confidence intervals, (iii) systematic cross-checks of binned
and unbinned analyses on mock and real data, and (iv) the use of mock data
including stellar contamination to test the impact on reconstructed signals.
Our analysis provides updated values for the dark matter content of 8
`classical' and 13 `ultrafaint' dSphs, with the quoted uncertainties directly
linked to the sample size; the more flexible parametrisation we use results in
changes compared to previous calculations. This translates into our ranking of
potentially-brightest and most robust targets---viz., Ursa Minor, Draco,
Sculptor---, and of the more promising, but uncertain targets---viz., Ursa
Major 2, Coma---for annihilating dark matter. Our analysis of Segue 1 is
extremely sensitive to whether we include or exclude a few marginal member
stars, making this target one of the most uncertain. Our analysis illustrates
challenges that will need to be addressed when inferring the dark matter
content of new `ultrafaint' satellites that are beginning to be discovered in
southern sky surveys.Comment: 19 pages, 14 figures, submitted to MNRAS. Supplementary material
available on reques
Preclinical Pharmacokinetics, Pharmacodynamics and Safety of Sucroferric Oxyhydroxide.
Sucroferric oxyhydroxide (VELPHORO(®)) is a polynuclear iron-based phosphate binder recently approved for the treatment of hyperphosphataemia in patients with chronic kidney disease (CKD). As a number of the available phosphate binders do not provide the optimal combination of good efficacy, adequate tolerability and low pill burden, sucroferric oxyhydroxide constitutes a promising alternative. Among the attributes of an ideal phosphate binder is minimal absorption and, hence, low risk of systemic toxicity. Accordingly, the iron-releasing properties and absorption, distribution, metabolism and excretion (ADME) profile of sucroferric oxyhydroxide, as well as the possibility of iron accumulation and toxicity, were investigated in a series of preclinical studies. The effect of sucroferric oxyhydroxide on the progression of vascular calcification was also investigated. Sucroferric oxyhydroxide exhibited a high phosphate-binding capacity and low iron-releasing properties across the physiological pH range found in the gastrointestinal tract. In the ADME studies, uptake of (59)Fe-radiolabelled sucroferric oxyhydroxide was low in rats and dogs (<1% from a 50 mg Fe/kg bodyweight dose), with the majority of absorbed iron located in red blood cells. Long-term (up to 2 years) administration of sucroferric oxyhydroxide in rats and dogs was associated with modest increases in tissue iron levels and no iron toxicity. Moreoever, in uraemic rats, sucroferric oxyhydroxide was associated with reduced progression of vascular calcification compared with calcium carbonate. In conclusion, sucroferric oxyhydroxide offers a new option for the treatment of hyperphosphataemia, with a high phosphate-binding capacity, minimal iron release, and low potential for iron accumulation and toxicity
Joint H.E.S.S. and Fermi-LAT analysis of the region around PSR J1813-1749
HESS J1813-178 is one of the brightest sources detected during the first HESS
Galactic Plane survey. The compact source, also detected by MAGIC, is believed
to be a pulsar wind nebula powered by one of the most powerful pulsars known in
the Galaxy, PSR J1813-1749 with a spin-down luminosity of . With its extreme physical
properties, as well as the pulsar's young age of 5.6 kyrs, the -rays
detected in this region allow us to study the evolution of a highly atypical
system. Previous studies of the region in the GeV energy range show emission
extended beyond the size of the compact H.E.S.S. source. Using the archival
H.E.S.S. data with improved background methods, we perform a detailed
morphological and spectral analysis of the region. Additionally to the compact,
bright emission component, we find significantly extended emission, whose
position is coincident with HESS J1813-178. We reanalyse the region in GeV and
derive a joint-model in order to find a continuous description of the emission
in the region from GeV to TeV. Using the results derived in this analysis, as
well as X-ray and radio data of the region, we perform multi-wavelength
spectral modeling. Possible hadronic or leptonic origins of the -ray
emission are investigated, and the diffusion parameters necessary to explain
the extended emission are examined.Comment: 8 pages, 4 figures, 1 table, In proceedings of ICRC202
Sustainability in astroparticle physics
The topic of sustainability is becoming increasingly important in research activities in astroparticle physics, both in existing and also in future instrument. At this year\u27s International cosmic ray conference (ICRC 2021) one session was dedicated to this topic. This publication will summarise the findings of this well-attended online session
Actions of the braid group, and new algebraic proofs of results of Dehornoy and Larue
This article surveys many standard results about the braid group with
emphasis on simplifying the usual algebraic proofs.
We use van der Waerden's trick to illuminate the Artin-Magnus proof of the
classic presentation of the algebraic mapping-class group of a punctured disc.
We give a simple, new proof of the Dehornoy-Larue braid-group trichotomy,
and, hence, recover the Dehornoy right-ordering of the braid group.
We then turn to the Birman-Hilden theorem concerning braid-group actions on
free products of cyclic groups, and the consequences derived by Perron-Vannier,
and the connections with the Wada representations. We recall the very simple
Crisp-Paris proof of the Birman-Hilden theorem that uses the Larue-Shpilrain
technique. Studying ends of free groups permits a deeper understanding of the
braid group; this gives us a generalization of the Birman-Hilden theorem.
Studying Jordan curves in the punctured disc permits a still deeper
understanding of the braid group; this gave Larue, in his PhD thesis,
correspondingly deeper results, and, in an appendix, we recall the essence of
Larue's thesis, giving simpler combinatorial proofs.Comment: 51`pages, 13 figure
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